The cardiac myocyte has long been the primary focus of most studies attempting to elucidate the signaling mechanisms underlying heart failure. More recently the involvement of nonmyocytes has emerged as potentially just as important as myocytes in contributing to and controlling cardiac remodeling and progressive pathogenesis in heart failure. Specifically, the cardiac fibroblast and its ability to convert to myofibroblasts in promoting the fibrotic response and ventricular remodeling appears to be a highly underappreciated disease process with significant ramifications. Fibroblasts are activated in the heart in response to damage or due to neuroendocrine signaling, such as through Transforming Growth Factor Beta (TGFp). Here we hypothesize that the fibroblast responds to TGFp and other cytokines through select signaling pathways in promoting the fibrotic response and maladaptive remodeling in heart failure. We will examine both canonical (Smad2/3) and non-canonical (TAK1/p38a) TGFp signaling within fibroblasts to determine how these cells and their activation mediate disease in heart failure. All previous in vivo analyses of TGFp signaling and cardiac fibrosis have focused on the myocytes given available genetic tools. However, we have recently engineered a novel fibroblast-specific knock-in mouse iinodel to permit tamoxifen-regulated Cre activity in vivo. We will use this mouse to study fibroblast-based signaling during the development of cardiac disease. Aim #1 will determine the necessary function of canonical TGFp signaling and Smad proteins in mediating cardiac fibrosis within the cardiac fibroblast itself. Aim #2 will exaniine the role that non-canonical TGFp signaling plays through TAKI and p38a MAPK in mediating cardiac fibrosis, andj once again, our focus will be on signaling within the cardiac fibroblast only. Aim #3 will examine a novel pathway that is calcium-TRPC6 activated and works in conjunction with TGFp signaling and other cytokines to pi^omote myofibroblast transdifferentiation in the heart and disease. These 3 specific aims will suggest for the first time the autonomous role for select signaling pathways from within the cardiac fibroblast in mediating myofibroblast transdifferentiation and fibrotic disease in the diseased heart. A number of potential therapeutic angles are suggested from the content of our project and emerging preliminary data. RELEVANCE (See instructions): Our work focuses on the cardiac fibroblast, a cell in the heart that is known to be important in the scarring processes and remodeling that occur after cardiac injury. We intend to study how this cell functions during these disease processes and attempt to modulate its actions so that we can impact favorably on cardiac disease and heart failure.